The present invention relates to a switching device and an operation method thereof, and more particularly, to a switching device including a solid electrolyte layer, and an operation method thereof.
Recently, researchers are studying to develop next-generation memory devices that can replace Dynamic Random Access Memory (DRAM) and flash memory.
Among such next-generation memory devices is a resistive memory device using a variable resistive material. The resistive memory device is capable of switching between at least two different resistive states as resistance varies drastically according to an applied voltage. The resistive memory device stores different data, which is bit data ‘0’ or ‘1,’ based on a resistance change of the variable resistive material. As for the resistive material having such characteristic, a transition metal oxide is generally used.
When a solid electrolyte material is interposed instead of a transition metal oxide in the same device as a resistive memory device, the switching mechanism may be different from that of the memory device using a transition metal oxide. Regardless, since the device using a solid electrolyte material also has a characteristic of switching between different resistance states according to an applied voltage, different data may be stored based on the switching characteristic. In this aspect, the device using a solid electrolyte material may be regarded as a resistive memory device in a broad sense. Hereafter, the device using a solid electrolyte material will be described in detail.
FIG. 1 is a cross-sectional view showing a conventional switching device including a solid electrolyte layer. Referring to FIG. 1, the conventional switching device includes a lower electrode 11, an upper electrode 13, and a solid electrolyte layer 12. When a negative voltage is applied to the lower electrode 11 and a positive voltage is applied to the upper electrode 13, metal ions are reduced in being transferred from the upper electrode 13 to the lower electrode 11 through the solid electrolyte layer 12 to thereby form a metal filament, which is a conductive path, in the solid electrolyte layer 12. Accordingly, the switching device turns into an on state, which is a state that the solid electrolyte layer 12 has a low resistance.
When a positive voltage is applied to the lower electrode 11 and a negative voltage is applied to the upper electrode 13, the metal filament of the solid electrolyte layer 12 is oxidized and metal ions are transferred to the upper electrode 13 to thereby remove the conductive path. Accordingly, the switching device turns into an off state, which is a state that the solid electrolyte layer 12 has a high resistance.
Two-state data may be stored in the solid electrolyte layer 12 by defining the state that the solid electrolyte layer 12 has a low resistance and the state that the solid electrolyte layer 12 has a high resistance as bit data ‘1’ and ‘0,’ respectively. In short, the switching device may be used as a memory device.
However, the switching device including the solid electrolyte layer 12 has the following drawbacks.
First, widely known and used solid electrolyte materials are GexSey, where Ge denotes germanium; Se denotes selenide; and x and y denote positive numbers, and GexSy, where S denotes sulfide; and x and y denote positive numbers. Since the solid electrolyte materials like GexSey and GexSy have high solubility, a switching device using such solid electrolyte material becomes sensitive to temperature and has low operation voltage. When the switching device is sensitive to temperature, transfer of ions becomes faster as temperature goes up. This may lead to an instable on/off state. On the other hand, when the operation voltage of the switching device is too low, it is hard to control the on/off state of the switching device.
In addition, since the switching operation is performed based on oxidation and reduction of metal ions, the switching speed is relatively slow.